Positron emission tomography (PET) has tremendous potential as a method of imaging blood flow to the heart in three dimensions. Its use has been limited by the need for an on-site cylotron. We tested the physiological characteristics of managnese 52m which is available from a generator that can be shipped conveniently. We found it was as good an indicator of myocardial blood flow as the standard tracers used, thatllium 201 and rubidium 82. Therefore, manganese 52m will be a useful redionuclide for use in myocardial scanning with the Pet scanner.